Unit I COLLOIDAL DISPERSION

COLLOIDAL DISPERSIONS
R.VIJAYAKUMAR ,M Pharm.,
1
R VIJAYAKUMAR., M Pharm.Asst
Professor, VCP.,Erode-12.

 Colloidal system is dispersion where in internal
phase dispersed particles are distributed uniformly
in a dispersion medium (External/continuous
Phase).
 Particle size-0.5 to 1 micron
 In colloidal systems particles pass through filter
paper but do not pass through semi permeable
membrane diffuse very slowly.
Example: Gelatin Acacia and Rubber
2

 Colloidal systems encountered in pharmacy :
Surfactant Micelles
Suspensions (may Be > 1 mm)
Emulsions (may Be > 1 mm)
Inhalation Aerosols
Suspensions Of Microorganisms
CLASSIFICATION OF COLLOIDAL SYSTEMS
ACCORDING TO PARTICLE SIZE
 Molecular dispersion
 Colloidal dispersion
 Coarse dispersion
3

 Therapy---
Colloidal system are used as therapeutic agents in
different areas. e.g- Silver colloid-germicidal Copper
colloid-anticancer Mercury colloid-Antisyphilis
 Stability
e.g. lyophobic colloids prevent flocculation in
suspensions.
e.g- Colloidal dispersion of gelatin is used in coating
over tablets and granules which upon drying leaves a
uniform dry film over them and protect them from adverse
conditions of the atmosphere. 4

 Absorption---
As colloidal dimensions are small enough, they
have a huge surface area. Hence, the drug
constituted colloidal form is released in large
amount.
 Targeted Drug Delivery---
Liposomes are of colloidal dimensions and are
preferentially taken up by the liver and spleen.
5

 Dispersed systems consist of particulate matter (dispersed phase),
distributed throughout a continuous phase (dispersion medium).
 They are classified according to the particle diameter of the
dispersed material.
 Molecular dispersions (less than 1 nm)
Particles invisible in electron microscope
Pass through semipermeable membranes and filter paper
Particles do not settle down on standing Undergo rapid
diffusion
Eg. ordinary ions, glucose Dispersed
Systems
6

 Colloidal dispersions (1 nm - o.5 um) –
Particles not resolved by ordinary microscope, can
be detected by electron microscope.
Pass through filter paper but not pass through
semipermeable membrane.
Particles made to settle by centrifugation
Diffuse very slowly
E.g. colloidal silver solutions, natural and synthetic
polymers.
7

 Coarse dispersions (> 0.5 um)
Particles are visible under ordinary
microscope
Do not pass through filter paper or
semipermeable membrane.
Particles settle down under gravity -
Do not diffuse
E.g. emulsions, suspensions, red blood
cells.
8

 1. Particle size:
This influence colour of dispersion. Wavelength of
light absorbed α 1/ Radius (small wave length)VIBGYOR
(large wavelength).
9

 2. Particle shape:
Depends on the preparation method and
affinity of dispersion medium This influence colour
of dispersion.
Shapes- spherical, rods, flakes, threads,
ellipsoidal.
Gold particles- spherical (red), disc (blue).
10

 3. Surface area:
Particle size small- large surface area
Effective catalyst, enhance solubility.
11

 4.Surface charge:
Positive (+)= gelatin, aluminum.
Negative (-) = acacia, tragacanth.
Particle interior neutral, surface charged.
Surface charge leads to stability of colloids because
of repulsions.
12

 Based of physical state of dispersed phase an dispersion
medium.
 Based of nature of interaction between dispersed phase and
dispersion medium.
 Based on molecular size in the dispersed phase.
 Based on appearance of colloids.
 Based on electric charge on dispersion phase.
13

14

1. LYOPHILIC COLLLOIDS
2. LYOPHOBIC COLLOIDS
3. ASSOCIATION COLLOIDS
15

 Colloidal solution in which the dispersed phase has a great
affinity for the dispersion medium. They are also termed as
intrinsic colloids.
 Such substances have tendency to pass into colloidal solution
when brought in contact with dispersion medium.

 If the dispersion medium is water, they are called hydrophilic or
emulsoids.
 The lyophilic colloids are generally self- stabilized.
 Reversible in nature and are heavily hydrated.
Examples are starch, gelatin, rubber, protein etc.
16

 Colloidal solutions in which the dispersed phase has no affinity to the
dispersion medium.
 These are also referred as extrinsic colloids.
 Such substances have no tendency to pass into colloidal solution when
brought in contact with dispersion medium.
 The lyophobic colloids are relatively unstable.
due to they are irreversible by nature and are stabilized by adding small
amount of electrolyte.
 They are poorly hydrated.
 If the dispersion medium is water, the lyophobic colloids are called
hyrophobic or suspenoids.
Examples: sols of metals like Au, Ag, sols of metal
hyroxides and sols of metal sulphides 17

 These colloids behave as normal electrolytes at low
concentrations but behave as colloids at higher concentrations.
 These associated colloids are also referred to as micelles.
 Sodium stearate behave as electrolyte in dilute solution but
colloid in higher concentrations.
Examples: Soaps , higher alkyl sulphonates
, polythene oxide.
18

MULTI MOLECULAR COLLOIDS Individual particles of the
dispersed phase consists of aggregates of atoms or small
molecules having diameter less than 10-7cm .
The particles are held by weak vander waal’s forces.
Example; gold sol, sulphur sol.
MACRO MOLECULAR COLLOIDS The particles of
dispersed phase are sufficiently large in size enough to be of
colloidal solution. These are called Natural Polymers.
Examples are starch, cellulose and proteins.
19

SOLS
 When a colloidal solution appears as fluid.
 The sols are generally named as dispersion medium.
 When the dispersion medium is water, the sol is known as
hydrosol or aquosol.
 When the dispersion medium is alcohol or benzene
it is called alcosol and benzosol respectively.
GELS
 When a colloidal solution appear as solid.
 The rigidity of gel varies from substance to substance.
 Examples : jelly, butter, cheese, curd.
20

 POSITIVE COLLOIDS
 When dispersed phase in a colloidal solution
carries a positive charge.
Examples : Metal hyroxides like
Fe(OH)3 , Al(OH)2 , methylene blue sol etc.
 NEGATIVE COLLOIDS
 When dispersed phase in a colloidal solution
carries a negative charge.
Examples : Ag sol, Cu sol
21

 PHYSICAL Properties
 OPTICAL Properties
 KINETIC Properties
 ELECTRICAL Properties
22

 Heterogeneity:
Colloidal solutions consist of two phases-dispersed phase and dispersion
medium.
 Visibility of dispersed particles:
The dispersed particles present in them are not visible to the naked eye and
they appear homogenous.
 Filterability:
The colloidal particles pass through an ordinary filter paper.
However, they can be retained by animal membranes, cellophane membrane
and ultra filters.
 Stability:
Lyophilic sols in general and lyophobic sols in the absence of substantial
concentrations of electrolytes are quite stable.
 Colour:
The colour of a colloidal solution depends upon the size of colloidal
particles present in it. 23
R VIJAYAKUMAR., M Pharm.Asst Professor, VCP.,Erode-12.

 When an intense converging beam of light is passed
through a colloidal solution kept in dark, the path of the
beam gets illuminated with a bluish light.
 The Tyndall effect is due to the scattering of light by
colloidal particles.
 Tyndall effect is not exhibited by true solutions. This is
because the particles present in a true solution are too
small to scatter light.
24
R VIJAYAKUMAR., M Pharm.Asst Professor, VCP.,Erode-1

 Used to observe tyndall effect,
 Dispersed particles appear as bright spots in dark
back ground this capable of yielding pictures of
actual particles size, shape and structure of
 Used to determine zeta potential.
25

 depend on tyndall effect.
used to give information about particle size and shape and for determination
of molecular weight of colloids.
Used to study proteins, association colloids and lyophobic sols.
Scattering described in terms of turbidity T.
 Turbidity: the fractional decrease in intensity due to scattering as the
incident light passes through 1 cm of solution.
 Turbidity is proportional to the molecular weight of lyophilic colloid Optical
Properties of Colloids.
Hc / T = 1/M + 2Bc
T: turbidity
C: conc of solute in gm / cc of solution
M: molecular weight B: interaction constant
H: constant for a particular system 26

 The continuous zigzag movement of the colloidal particles in
the dispersion medium in a colloidal solution is called
Brownian movement.
 Brownian movement is due to the unequal bombardments of
the moving molecules of dispersion medium on colloidal
particles.
 The Brownian movement decreases with an increase in the
size of colloidal particle.
 This is why suspensions do not exhibit this type of movement.
27R VIJAYAKUMAR., M Pharm.Asst Professor, VCP.,Erode-12.

28
 This brownian motion arises due to the uneven distribution
of the collisions between colloid particle and the solvent
molecules.
 Brownian movement was more rapid for smaller particles.
 It decrease with increase the viscosity of the medium.

 Particles diffuse spontaneously from a region of higher
concentration to one of lower concentration until the
concentration of the system is equilibrium.
 Diffusion is a direct result of Brownian movement.
29

 Ficks Ist law: states that particles diffuse spontaneously
from a region of high concentration to region of low
concentration until diffusion equilibrium is attained.
dq = -Ds (dc/dx) dt
Dq = quantity of drug diffused
D = diffusion coefficient
S = plane area
dC = concentration change
dx = distance travelled
Dt = time taken for diffusion
Application: molecular weight determination.
30

 The velocity v of sedimentation of spherical particles having a
density ρ in a medium of density ρo and a viscosity is given by
stokes‘s Law
v = d2 (ρi-ρe)g/18η
V = rate of sedimentation
D = diameter of particles
ρ = density of internal phase and external phase
g = gravitational constant
η = viscosity of medium
 This law obeys only if the particles should be spherical
 Stokes equation about only 5μm.
 Brownian movement becomes active sedimentation will becomes
slow due to gravity, promotes mixing.
 A strong force must be applied to bring sedimentation
 Ultracentruge is used for the complete sedimentation
 Ultracentrifuge can produce a force one million times that of
gravity R VIJAYAKUMAR., M Pharm.Asst
Professor, VCP.,Erode-12. 31

 Applications:
 1. Molecular weight estimation
 2. Study micellar properties of drug.

 van 't hoff equation:
π = cRT
 Can be used to determine the molecular weight of
colloid in dilute solution.
(where C = the grams of solute / liter of solution, M =
molecular weight)
π/C = RT/M Kinetic Properties of Colloids
π = osmotic pressure
R= molar gas constant

 It is the resistance to flow of system under an applied
stress.
 The more viscous a liquid, the greater the applied
force required to make it flow at a particular rate.
 The viscosity of colloidal dispersion is affected by
the shape of particles of the disperse phase
 Spherocolloids dispersions of low viscosity
 Linear particles more viscous dispersions

 Surface charge
 Electrical double layer
 Zeta potential
 ELECTROPHORESIS
 Electro-osmosis
 Sedimentation Potential (donnan effect)
 Steaming Potential

Surface charge: The particles of a colloidal solution are electrically
charged and carry the same type of charge, either negative or positive.
 The colloidal particles therefore repel each other and do not cluster
together to settle down.
 The charge on colloidal particles arises because of the dissociation of
the molecular electrolyte on the surface.
37

Particles within a colloidal dispersion carry charges
that contribute to the net charge of a particle.
Used in predicting stability of colloidal dispersion.

 The movement of colloidal particles towards a particular
electrode under the influence of an electric field.
 If the colloidal particles carry positive charge, they move
towards cathode when subjected to an electric field and vice
versa.
40

 It is the opposite in principal to that of electrophoresis.
 When electrodes are placed across a clay mass and a direct
current is applied, water in the clay pore space is transported
to the cathodically charged electrode by electro-osmosis.
 Electro-osmotic transport of water through a clay is a result of
diffuse double layer cations in the clay pores being attracted
to a negatively charged electrode or cathode.
 As these cations move toward the cathode, they bring with
them water molecules that clump around the cations as a
consequence of their dipolar nature.

 The movement of dispersion medium under the influence of
an electric field in the situation when the movement of
colloidal particles is prevented with the help of a suitable
membrane.
 During electrosmosis, colloidal particles are checked and it is
the dispersion medium that moves towards the oppositely
charged electrode.

 The sedimentation potential also called the ( Donnan
membrane effect).
 It is the potential induced by the fall of a charged particle
under an external force field.
 It is analogous to electrophoresis in the sense that a local
electric field is induced as a result of its motion.
 if a colloidal suspension has a gradient of concentration (such
as is produced in sedimentation or centrifugation), then a
macroscopic electric field is generated by the charge
imbalance appearing at the top and bottom of the sample
column.

R VIJAYAKUMAR., M Pharm.Asst Professor, VCP.,Erode-12. 44

 Differs from electro-osmosis in that the potential is created
by forcing a liquid to flow through a bed or plug of particles.

 Breakage of potential energy barrier leads to precipitation/
agglomeration.
 Instability Methods:
 1. Reducing height of potential barrier.
 2. Increasing the kinetic energy, reduces potential energy.
Instability reasons:
 1. Removal of electrolyte (1% minimum)
 2. Addition of electrolyte (2%minimum)
 3. Addition of electrolytes of opposite charge (2% minimum)
4. Addition of oppositely charged colloid (2% minimum).

1.Removal of electrolyte (1% minimum)
Colloids + electrolytes ^ stable colloidal dispersion
Dialysis = remove Electrolytes --- Particles coagulate
^Settle to bottom.
2.Addition of electrolyte (2% minimum)
Stable colloidal dispersion + excess electrolyte
electrolyte --- Accumulate ^instability.
3. Addition of electrolytes of opposite charge (2% minimum)
Stable colloidal dispersion + electrolyte opposite charge --
attractions between particles ^ Flocculation of particles.
Schulze-Hardy Rule: Precipitating power α ionic charge
Al+3>Ba+2>Na+ So4 -2>Cl
4. Addition of oppositely charged colloid (2% minimum)
Bismuth colloids (+) + Tragacanth colloids (-)
^Coagulation. R VIJAYAKUMAR., M Pharm.Asst Professor, VCP.,Erode-12. 47

 1- Addition of large amounts of electrolytes - Anions arranged
in a decreasing order of precipitating power: citrate > tartrate
> sulfate > acetate > chloride> nitrate > bromide > iodide.
 The precipitation power is directly related to the hydration of
the ion and its ability to separate water molecules from
 2- Addition of less polar solvent - e.g. alcohol, acetone
The addition of less polar solvent renders the solvent mixture
unfavourable for the colloids solubility.

 Coacervation is the process of mixing negatively and
positively charged hydrophilic colloids, and hence the
particles separate from the dispersion to form a layer rich in
the colloidal aggregates (coacervate).

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Unit I COLLOIDAL DISPERSION

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